Dog heat cycle 101: Everything you need to know about the dog reproduction cycle

There are many myths and misconceptions about the dog heat cycle and dog reproduction in general.

New dog owners often have lots of questions: When to expect the first heat? How often do dogs go into heat? How long does it last? When is the best time to breed your dog? Do male dogs go into heat? And let’s not forget spaying, which deserves its own separate article.

In this blog post, I will  answer the most common questions regarding dog heat and reproduction. 

Ready? So let’s dive in… ☺️

While I am a veterinarian, this article is not intended to replace professional veterinary advice. If you have any medical concerns about your pet, consult your vet immediately. Always seek professional assistance if you are unsure of your pet’s health.

This post may contain affiliate links, which means I may receive a commission, at no extra cost to you, if you make a purchase through a link. Please see my full disclosure for further information.

two dogs sleeping together

Do dogs get periods?

Let’s just start with this common question. I have to say I do understand the confusion. There are hormonal changes involved, there is bleeding and it’s all somehow part of the reproduction cycle. However, a woman’s period and a dog in heat are two completely different things.

The menstrual cycle is the monthly hormonal cycle a woman’s body periodically goes through to prepare for pregnancy. There are several hormones involved and it’s a very complex process. Ovulation is the time when a woman is fertile. During ovulation, the egg is released from the ovaries and can be fertilized. To prepare the body for pregnancy, estrogen and progesterone cause the lining of the uterus to build up. If the egg wasn’t fertilized, and therefore there is no pregnancy, progesterone levels drop, causing the uterus lining to shed. This is what we call menstruation or period. The bleeding a woman experiences every month is because she didn’t get pregnant during her ovulation and her uterus is shedding its lining.

Now, a female dog in heat is in the fertile phase of her reproduction cycle.

It’s the phase when the eggs are released from the ovaries and can be fertilized. This means that a dog can get pregnant only when she is in heat.

What are the signs your dog is in heat?

The earliest sign is the swelling of the vulva.
However, most owners perceive the bloody vaginal discharge as a first sign. It can be bloody at first and will change to watery and pinkish-red after a few days.

A dam in heat will often urinate more frequently than normal. She may develop marking behavior, where she urinates small amounts on various objects when out on a walk or even at home. The urine contains pheromones that signal to male dogs she is in the reproductive stage of her cycle and willing to mate.

Male dogs can smell a dam in heat from a distance and are willing to go to great lengths to mate with her. So be prepared and check your fence thoroughly 😉

Some dogs can suddenly jump over fences they normally wouldn’t jump over. This is true not just for male dogs, but for your female as well. So be sure to secure your house not just from male dogs trying to get inside, but also from your own dam trying to get out.

She might also change her behavior and become more nervous, agitated, or needy. Or be overly friendly with other dogs, mount or hump, and turn her tale to the side.

Signs of dog heat:

  • swelling of the vulva
  • bloody vaginal discharge
  • frequent urination
  • marking behavior
  • attracting males
  • changes in behavior
  • mating behavior

How long is each dog heat cycle?

The dog heat cycle lasts usually around 18-21 days, but this can (and usually does) vary individually. So be prepared for anything between 2-4 weeks.

The 4 stages of the dog reproduction cycle

Let’s talk a bit about physiology. The dog reproductive cycle has 4 stages. 

→ Proestrus

The first stage of dog heat cycle is called proestrus. There is mild swelling of the vulva and bloody discharge. Your dam might attract males during this phase, but is not ready to breed yet. She might even get aggressive and attack male dogs that will go near her.

→ Estrus

The second phase is called estrus. This is the mating period of the heat cycle. The discharge is usually lighter, watery, and pinkish-red. The vulva is swollen, enlarged, and soft. Your dam is willing to mate and is in her fertile phase. This is the optimum time for breeding.

→ Diestrus

After the estrus comes diestrus. The vulva returns to its normal size and the discharge might become redder. Your dam will no longer accept or tolerate mating attempts of male dogs. The heat ends when all signs of discharge and swelling disappear. Diestrus can last for 60-90 (if your dam is not pregnant) or until she gives birth.

→ Anestrus

The last phase of dog heat cycle is anestrus. This is the time between the end of her last heat and the beginning of the next proestrus. So basically the rest of the year 🙂

How long each phase lasts depends on the individual. On average, proestrus can last for about 9 days (give or take a few days). Estrus can last for 3-11 days.

digital litter charts for dog breeders

How to determine when is the best time to mate my dog?

Well, this can be quite difficult.

You cannot determine the best time for breeding based only on signs of heat.

For most females, the best time for breeding is between the 10th and 14th day of estrus.

I know there are a lot of dog heat calculators, but they are based on the average duration of a dog heat cycle. However, some females ovulate as early as the third or fourth day or as late as the eighteenth day.

So if you want to be sure about the optimum time, you need to work closely with your vet. The best time for mating can best be determined using a combination of various methods (blood tests, vaginal inspection, cytology…)*. This sometimes means you need to make more than just one trip to a vet. 

dog heat cycle

When does the heat start?

Dogs will have their first estrus when they reach puberty. This can vary by breed – smaller breeds can reach puberty much sooner than big breeds. Some dogs can go into heat as young as 4 months old, but the average is around 6 months of age. Some giant breeds need a bit more time with up to 18-24 months.

So all in all, it can be at 4-6 months, but don’t stress if your almost 1-year-old pup didn’t go into heat yet.

Once it starts, it may take some time for the cycle to become regular.

Even if your dog is in heat for the first time and has reached puberty, she is not ready to get pregnant yet. Her body (and her eggs) are not mature enough, it’s better to wait with any breeding plans after the second estrus cycle. Even better yet, your vet can tell you when your dog is mature enough to get pregnant.

dog heat cycle

How often do dogs go into heat?

This depends on the breed. Small dogs can go in heat sometimes even 3 times per year, giant breeds usually only once. The average is 2 times per year.

How to help a dog in heat

If your dam is in heat, she might need a bit of extra attention. Long walks, play, and cuddling might help her relax.

You can create a nest for her with old bathroom towels that will catch the blood.

There are also plenty of different dog heat diapers to choose from. You just need to find the one that your dog can tolerate and you are ok with.

Let’s try a little exercise. Picture this scenario: your dog starts bleeding, she’s nervous, and needs to pee often. You’re running behind her with paper towels, trying to keep your floor (and your bed, couch…) clean. You dash to the store and buy some dog diapers. After 30 minutes of active resistance, you finally wrestle your now very agitated girl into a diaper. However, the moment you turn your back, the diaper is shredded into teeny tiny pieces all over your living room. While this is an extreme example, it’s not far from the truth for some dog owners.

To avoid this chaos, I recommend training with doggie diapers before your dog goes into heat. This way, you’ll know which product works best for you, and your dog won’t be stressed by suddenly having to tolerate a diaper on top of being hormonal. Treat it like any other training – with loving attention, yummy treats, and a great deal of patience 🙂

Do male dogs go into heat?

The short answer is no ☺️

Male dogs don’t go into heat, “in heat” specifically refers to the female dog reproduction cycle.

Once male dogs reach puberty and become fertile, they are capable of mating year-round.

However, what owners sometimes notice are behavioral changes when there are dogs in heat nearby. Sometimes the owners are not aware that there is a dam willing to mate somewhere in the vicinity, but the dog knows. Keep him distracted as best as you can with long walks, plenty of exercises, and physical activity.

Having a female dog comes with great responsibility. Unwanted puppies and dog overpopulation are common problems everywhere.

You need to decide if you want to breed your dog or if it would be better to spay her. If you decide to spay your dog, talk to your vet. They will explain the procedure and all the pros and cons.

If you choose not to spay your dog but don’t want puppies (or don’t want puppies yet), you’ll need to be extra vigilant during her heat. Dogs are willing to mate even with close relatives, so keep fathers and sons separate from the females. Also, keep your house secure and be careful when walking your dog. Don’t let her roam free, not even in a small dog park. A long leash is your best friend at this time. 🙂

One more thing I need to mention:

If your dog accidentally mates with another dog, call your vet as soon as possible. There are injections that can be used within a day or two after mating, but there are some risks involved. Talk to your vet for advice.

I hope this answered your questions about the dog heat cycle and how to help your dam when she’s “hormonal” 🙃

If you want to learn more about pet health, you can sign up for my newsletter. Now you can get a free pet care planner as a bonus 🙂



  • Sandra Ans

    Thank you for this post! It was a very interesting and useful read cause my mom is having a small Chihuahua female and it’s the first time when we are going through the dog heat. My family always had male dogs and never were stressed about ”female things”. 😀
    Thank you so much also for your blog! You do a great job! ♥

    • Monika

      Thank you!🤗 I know it can be a bit confusing, especially for first-time owners when they are suddenly dealing with “female things” (love the expression btw. 😊 ). I hope this article will help.

Leave a Reply

Your email address will not be published. Required fields are marked *